WATER FILTRATION TECHNIQUE REMOVES DANGEROUS FRESHWATER ALGAE
TOXINS

COLUMBUS , Ohio  A water filtration technique that normally
cleans up agricultural chemicals is also effective at removing
a toxin secreted by algae found in lakes and rivers, an Ohio
State University study has found.

Harold
Walker

Engineers here determined that the technique greatly outperformed
other methods by removing at least 95 percent of a toxin secreted
by Microcystis, a blue-green algae.

Microcystis is native to freshwater lakes and rivers
around the country, and secretes toxins that can cause liver
damage in animals including humans. Worsening environmental pollution
in Lake Erie during the last decade has caused algal blooms,
the most recent of which began this August.

Some 13 million people rely on Lake Erie for their water supply,
so Microcystis is a growing concern there, Walker said.
But dangerous algal blooms have occurred across the country this
summer, from Massachusetts to California .

And while many water filtration plants are beginning to use
high-tech ultrafiltration membranes with very fine holes to filter
water, Microcystin toxins are small enough to slip through.
For example, the toxin used in this study was microcystin-lr,
a tiny molecule made up of only seven amino acids.

Rather than invent a new technology for filtering microcystin-lr,
Walker and his colleagues decided to test whether combining activated
carbon with membrane filters would do the trick. That technology
has already proven effective for removing herbicides and pesticides
from drinking water.

"This toxin is an organic molecule, and we knew that
activated carbon is good at removing organics," Walker said,
"so we coupled the carbon with membranes. Together, they
provide a way for water treatment plants to remove the toxin
by basically upgrading the membrane system they already have."

"Microcystis secretes
a whole range of toxins, and we only looked at the one we thought
would be the most important for health reasons. Then there's
a whole host of other toxic algae that secrete their own toxins.
I suspect this technology would be pretty effective for all these
toxins."

Water treatment plants that already had membranes in place
could add carbon to their systems without purchasing new equipment,
he added.

Activated carbon is a highly porous form of charcoal that
sticks to organic molecules. It's often used to filter water
and clean up environmental spills, and it's even administered
to poison victims to clean toxins from the digestive tract.

The engineers combined the active carbon with three different
commercially available membrane filters to remove microcystin-lr
from samples of Lake Erie drinking water. Each combination produced
good results: one removed 95 percent of the toxin, one removed
97 percent, and the other removed 99 percent. Without the carbon,
even the most effective ultrafiltration membrane removed only
78 percent of the toxin.

This is the first time this technique has been used to remove
an algal toxin, and Walker cautioned that more research needs
to be done before commercial water treatment plants could adopt
it wholesale.

"Microcystis secretes a whole range of toxins,
and we only looked at the one we thought would be the most important
for health reasons," he said. "Then there's a whole
host of other toxic algae that secrete their own toxins. And
we don't know if there are synergistic effects between the toxins.
Still, I suspect this technology would be pretty effective for
all these toxins."

He would like to start a pilot project with a water treatment
plant that uses membrane filters, ideally to test the system
during an algal bloom.

This work was funded by the Ohio
Sea Grant. PICA USA, Inc., of Columbus, OH, provided the
powdered activated carbon.